Engines may use variable valve operation, such as variable cam timing, to improve engine performance. In one example, oil control valves, such as spool valves or solenoid valves, may be used to adjust the position (e.g., angle) of the cams via hydraulic actuation of a cam phaser. Therefore, the valve timing may be advanced or retarded depending on the desired valve operation.
Degradation of an oil control valve may occur due to formation of particulates in the hydraulic fluid which may adhere to, or become trapped in, various parts of the valve. The trapped particles may block flow channels, thereby degrading or possibly inhibiting accurate control of oil control valve operation. This may degrade operation of the cams and therefore decrease the efficiency of the combustion process.
Various control strategies have been designed to clean the oil control valve. Such control strategies may be implemented at specified time intervals during engine operation, such as during Deceleration Fuel Shut Off DFSO, when fuel injection is not occurring, when the cam phaser is within a specified range away from the hard stops, and when the valves are substantially stationary. In U.S. Pat. No. 6,718,921, an oil control valve cleaning system and method are disclosed. Cleaning may be implemented, during a limited window of operation, when specified operating conditions are achieved such as non-operation of the fuel injection system, engine torque is within a predetermined range (e.g., below a threshold value), etc.
The inventors have recognized several problems with the above approach. First, the available window of cleaning operation according to such approaches may be very small. Moreover, the available window of operation may be further reduced in vehicles utilizing hybrid technology. For example, DFSO may not occur in a hybrid vehicle, but rather the engine may fully shut-down and come to rest.
As such, in one approach, a method for operating an oil control valve coupled to a cam phaser configured to adjust a position of at least one cam between hard stops, the oil control valve included in an internal combustion engine having an intake valve and/or an exhaust valve controlled via the cam phaser. The method including operating the oil control valve responsive to cam position feedback information, the oil control valve adjusted in a first relationship based on the feedback information and operating the oil control valve in a cleaning mode during select combustion conditions by abruptly switching the oil control valve between two states responsive to the cam position feedback information. The oil control valve adjusted in a second relationship based on the feedback information, the second relationship including more abrupt adjustment than the first relationship.
In this way, a robust valve cleaning strategy may be implemented over a wider range of operating conditions since active valve control may be achieved during the cleaning operation. Further, valve cleaning may be effectively performed during engine operation, thus increasing the available engine shut-down conditions for hybrid vehicle operation, if desired.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.